fix(m12): user can answer idea-questions — inline + bell support

Two gaps discovered during the first live grill-session of IDEA-002:
the agent posted a question, but the user had no UI to answer it.
1. Idea-questions only appeared on the Timeline-tab as read-only entries
2. Notifications-bell fetched + handled story-questions only

This fix:

**Inline answer-form in IdeaTimeline** (components/ideas/idea-timeline.tsx)
- Open questions now render an AnswerForm directly under the question text
- Multi-choice options become clickable buttons (one-click submit); free-text
  fallback via collapsed details/textarea
- Plain free-text questions render textarea + Verzend
- Calls existing answerQuestion server-action; toast + router.refresh on success

**Notifications-bell extended for idea-questions**
- stores/notifications-store.ts: NotificationQuestion → discriminated union
  (kind: 'story' | 'idea'); forYouCount treats idea-questions as always-for-you
  (idea is strictly user_id-only — only the owner sees them)
- components/notifications/notifications-bridge.tsx: parallel fetch of
  story-questions (productAccessFilter) + idea-questions (idea.user_id ===
  session.userId); merged + sorted by created_at
- components/notifications/notifications-sheet.tsx: renders idea_code/title
  for kind='idea'
- components/notifications/answer-modal.tsx: header + open-link branch on
  kind (idea → /ideas/[id]?tab=timeline; story → existing /sprint link)
- lib/realtime/use-notifications-realtime.ts: idea-question events also
  trigger close+reconnect on 'open' (loads fresh detail) and remove(id) on
  non-open — same pattern story-questions already use
- components/shared/notifications-bell.tsx: badge counts idea-questions as
  for-you regardless of assignee

**Security gap closed (actions/questions.ts answerQuestion)**
Before: accepted any answer if user has product-access.
After: idea-questions require idea.user_id === session.userId; story-
questions keep the existing productAccessFilter path. (Prisma 7 rejects
\`{ not: null }\` in WHERE; routing happens app-level after a single fetch.)

Tests: 546/546 still green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

stores/notifications-store.ts

@@ -12,19 +12,35 @@
 
 import { create } from 'zustand'
 
-export interface NotificationQuestion {
-  id: string
-  product_id: string
-  story_id: string
-  task_id: string | null
-  story_code: string | null
-  story_title: string
-  assignee_id: string | null
-  question: string
-  options: string[] | null
-  created_at: string
-  expires_at: string
-}
+// Story-questions en idea-questions delen het bel-paneel sinds M12 hotfix.
+// `kind` discrimineert; UI rendert label + link op basis daarvan.
+export type NotificationQuestion =
+  | {
+      kind: 'story'
+      id: string
+      product_id: string
+      story_id: string
+      task_id: string | null
+      story_code: string | null
+      story_title: string
+      assignee_id: string | null
+      question: string
+      options: string[] | null
+      created_at: string
+      expires_at: string
+    }
+  | {
+      kind: 'idea'
+      id: string
+      product_id: string
+      idea_id: string
+      idea_code: string
+      idea_title: string
+      question: string
+      options: string[] | null
+      created_at: string
+      expires_at: string
+    }
 
 interface NotificationsState {
   questions: NotificationQuestion[]
@@ -56,6 +72,11 @@ export const useNotificationsStore = create<NotificationsState>((set, get) => ({
 
   forYouCount: (userId) => {
     if (!userId) return 0
-    return get().questions.filter((q) => q.assignee_id === userId).length
+    return get().questions.filter((q) => {
+      // story-questions: assignee = jij; idea-questions: altijd voor jou
+      // (idee is strikt user_id-only en alleen jij ziet 'm).
+      if (q.kind === 'story') return q.assignee_id === userId
+      return true
+    }).length
   },
 }))